Milking of cows on a large scale is almost entirely done with a milking machine. The milking machine draws the milk from the cow's udder by pulsating vacuum, e.g. by attaching a teat cup connected to a vacuum pump and pulsating the vacuum to alternately allow the milk to fill and drain from the area of the udder and test to simulate hand milking of the cow. The tendency is to minimize the milking time by using high vacuum which causes irritation to the teat and udder.
The milk secreted through the teat canal is essentially sterile. However, contamination of the test environment is virtually unavoidable under normal field conditions, even when sterilized milking equipment is used. A wide variety of microorganisms can be present on or near the cow's udder and may even enter the teat canal, thus creating the possibility of infection.
The damage to tissue caused by the milking machine followed by exposure of the damaged tissue to certain microorganisms can result in an infection known as mastitis. This problem is of great economic importance to the dairy farmers because the infected cow's contaminated milk cannot be marketed. The infected udder must be treated with an antibiotic. However, the milk from such cows cannot be sold until the antibiotic is absent from the milk (usually about 3-5 days after the last treatment with the antibiotic).
According to experts, the dipping of tests in an antimicrobial (biostatic or biocidal) solution after milking is one of the most effective procedures that a dairy farmer can follow to prevent infections of the udder. An essential purpose of the teat dip is to prevent mastitis by killing or controlling the microorganisms and by helping heal any injured tissue. The teat dip product desirably has a wide spectrum of antibacterial activity to minimize infection, typically has emollient properties to promote healing and typically is or can be buffered to approximate "skin" pH, thereby minimizing irritation possibilities.